Description

This command lets the user activate or deactivate elements at a pre-defined time or on a certain signal.
If a FUNCTION is used an element is activated or deactivated on function values > 0.

The optional constant $0 \le \xi \le 1$ is used to scale the internal forces of unactivated elements.
$\xi$ is typically used in situations where nodes of unactivated elements are part of
a MERGE interface and where the nodes need to be active from time 0 to avoid the formation of gaps.
A typical application is weld seams where the weld elements need to follow
the deformation of the base material. Else they will not be activated at the correct location.